The invention relates to a tibia part for a knee joint prosthesis and to a kit for putting together a knee joint prosthesis. Furthermore, the invention relates to a method for implanting and for re-operating a knee joint prosthesis.
Knee joint prostheses usually comprise a tibia part, which is fixed in the tibia, a femur part, which is fixed in the femur, as well as a bearing body which is arranged between them and which is often designated as a meniscus part. The tibia part has a tibia bearing surface for the support of the bearing body. The bearing body is provided on its side which faces away from the tibia bearing surfacexe2x80x94that is, on the side facing the femurxe2x80x94with bearing shells which cooperate with condyles (running surfaces) of the femur part.
Nowadays knee joint prostheses are available in a large number of different prosthesis types, the functioning principles of which often differ strongly from one another. This is connected, among other things, with the fact that the prosthesis, depending on the state of the ligaments (cruciate ligaments, collateral ligaments), must wholly or partly take over the various functions of the ligaments in the respective patient.
Thus for example types of prostheses are known (see e.g. EP-A-0,923,916) in which the meniscus part is fixed to the tibia bearing surface of the tibia part, so that the meniscus part is arranged to be immobile relative to the tibia part.
Furthermore, prosthesis types are known in which the meniscus part is journalled on the tibia bearing surface so as to be movable relative to the tibia part, i.e. is thus either slidingly displaceable on the tibia bearing surface or is rotatable on the tibia bearing surface or both.
In EP-A-0,913,132 for example a knee joint prosthesis is shown in which the meniscus part is admittedly slidingly displaceable, but is however substantially rotationally fixedly seated on the tibia bearing surface of the tibia part, so that the meniscus part is admittedly displaceable on the tibia bearing surface in the anterior/posterior direction relative to the tibia part, but is substantially not rotatable.
Furthermore, prosthesis types are known in which the meniscus part is admittedly rotatable, but however not displaceably journalled on the tibia part relative to the tibia bearing surface, so that the meniscus part is only rotatable relative to the tibia part, but cannot be displaced.
Finally, prosthesis types are known from EP-A-0,519,873 in which the meniscus part is both slidingly displaceable and rotatable relative to the tibia bearing surface.
Moreover, prosthesis types are known in which means are provided in order to stabilize the femur part during the flexion (bending) in the posterior position relative to the meniscus part or relative to the tibia part respectively. This prosthesis type is used in particular when the rear cruciate ligament is no longer present or is no longer capable of functioning.
In particular in cases in which the collateral ligaments are no longer present or are no longer sufficiently capable of functioning, prosthesis types are used in which means for the lateral stabilizing (varus/valgus stabilizing) are provided.
From this non-exhaustive listing it is already clear that a large number of different embodiments of the individual components of a knee joint prosthesis, in particular also a large number of different tibia parts, must be provided in order that the respective prosthesis which is ideal for the respective patient can be put together.
For each prosthesis type there exists a tibia part which is specially matched to this type in order to ensure as good a cooperation with the remaining components of the prosthesis as possible. This means: A tibia part which was manufactured for a specific prosthesis type cannot as a rule be used for other prosthesis types. As a result of this there exist in part considerable constructional differences between tibia parts which belong to different prosthesis types.
This is however disadvantageous in particular from the point of view of the manufacturing technology, since for each prosthesis type the tibia part must be produced in accordance with a manufacturing process which is specific to the respective tibia part. Thus in order to provide a plurality of tibia parts for different prosthesis types, a plurality of partly very different, manufacturing processes must also be used, which is very complicated from the technical side and in addition is also economically disadvantageous.
If a kit is to be created by means of which different prosthesis types can be put together, then this kit must comprise a large number of tibia parts which differ from one another in regard to their functional design. Since in addition for each prosthesis type a plurality of tibia parts of different sizes must yet also be present in the kit in order to take into account the different anatomical circumstances of the patients, a kit of this kind necessarily comprises a very large number of individual components.
Here the invention wishes to provide a remedy. It is therefore an object of the invention to propose a tibia part which considerably simplifies the manufacture for different prosthesis types. Furthermore, through the tibia part a kit for the putting together of a knee joint prosthesis should be enabled which comprises considerably fewer different tibia parts without concessions therefore being necessary on the flexibility with respect to the different prosthesis types which can be realized with the kit or concessions on the functioning of the knee joint prosthesis.
In accordance with the invention thus a tibia part for a knee joint prosthesis is proposed which comprises a tibia bearing surface for the support of a bearing body (meniscus part) and a bore for the reception of a guiding element, with a cut-out for the rear cruciate ligament being provided in the tibia bearing surface and with the bore being formed in such a manner that it can, depending on the design of the guiding element, receive the latter either rotationally fixedly relative to the tibia part or rotatably relative to the tibia part.
These measures enable a tibia part which is suitable for a plurality of functionally different prosthesis types, which means that the same tibia part can be combined with different bearing bodies and/or femur parts and/or guiding elements in order thus to be able to put together different prosthesis types. Through the cut-out for the reception of the rear cruciate ligament the tibia part is suitable for prosthesis types in which the rear cruciate ligament remains intact and is capable of functioning. Through the design of the bore in the tibia bearing surface the tibia part in accordance with the invention is suitable both for prosthesis types in which the bearing body is rotationally fixedly seated relative to the tibia part and for prosthesis types in which the bearing body is rotatably journalled on the tibia bearing surface.
The variability of the tibia part in accordance with the invention or, respectively, its compatibility with different prosthesis types means a considerable simplification of the manufacturing process, since the same tibia part can be used for different prosthesis types.
The tibia part is preferably provided with an extension piece which serves for securing the tibia part in the tibia, with means being provided in order to connect the extension piece firmly to a separate anchoring shaft in the event that a separate anchoring shaft appears indicated as a result of the anatomical circumstances. Through this it is possible to provide the tibia part with differently designed anchoring shafts, in particular anchoring shafts of different lengths (insofar as indicated), in order thus to be able to match the anchoring of the tibia part in the tibia ideally to the special application.
In accordance with a first exemplary embodiment, securing means are provided at the tibia part in order to fix the bearing body on the tibia bearing surface. This exemplary embodiment is suitable in particular for prosthesis types in which the bearing body is immobile relative to the tibia part.
In a second exemplary embodiment these securing means are not provided, so that the bearing body is movably journalled on the tibia bearing surface relative to the tibia part.
In regard to a manufacturing process which is as simple as possible, it is advantageous when these two exemplary embodiments differ only through the securing means and are otherwise practically the same constructionally.
In accordance with a further aspect of the invention a kit for putting together a knee joint prosthesis is proposed. The kit comprises at least one tibia part having a tibia bearing surface and further comprises at least one bearing body which can be journalled on the tibia bearing surface and which has bearing shells on its side which faces away from the tibia bearing surface, as well as at least one femur part having condyles for cooperating with the bearing shells of the bearing body. The tibia part of this kit is formed as a tibia part in accordance with the invention, as has already been described above.
Since the tibia part in accordance with the invention is suitable for a plurality of functionally different prosthesis types, it is not necessary in a kit of this kind to provide a tibia part for every prosthesis type which is specially matched to this prosthesis type. Rather, the same tibia part can be combined with functionally different or functionally differently cooperating components (e.g. bearing bodies, femur parts, guiding elements) respectively without Concessions as regards the capability of functioning of the knee joint prosthesis being necessary for this. Through this, considerably fewer different tibia parts are required for the kit without the flexibility of the kit thereby being diminished in regard to the prosthesis types which can be put together. This represents a considerable simplification not only in relation to the number of the tibia parts which are contained in a kit, but also in the manufacturing technology.
In the kit preferably at least one tibia part and at least one bearing body are preferably formed in such a manner that the bearing body can be fixed to the tibia bearing surface in order that prosthesis types with a bearing body which is fixed relative to the tibia part can also be realized.
In order to realize prosthesis types with bearing bodies which are both displaceable and rotatable relative to the tibia part, the kit preferably comprises at least one bearing body which can be slidingly displaceably journalled on the tibia bearing surface and at least one guiding element which is designed as a connecting rod, the one end of which can be rotatably journalled in the bore of the tibia part and which has a guiding section which is formed and cooperates with the bearing body in such a manner that the bearing body is displaceable relative to the tibia bearing surface in the anterior/posterior direction.
For prosthesis types with a rotatablyxe2x80x94but not displaceablyxe2x80x94journalled bearing body at least one bearing body is preferably provided in the kit which has on its side facing the tibia bearing surface a molded on or fixed guiding element by means of which the bearing body can be rotatably journalled in the bore of the tibia part.
For prosthesis types with posterior stabilizing the kit preferably comprises at least one bearing body which has an axially through-going elongate hole and at least one guiding element which passes through the elongate hole of the bearing body, with the one end of the guiding element being formed as a pin which extends into the bore in the tibia part and is there rotatably journalled, and the other end protruding in between the condyles of the femur part and having a guiding surface for cooperating with a stabilizing element which is provided in the femur part.
Furthermore, for the cases in which the rear cruciate ligament and the collateral ligaments no longer exist or are no longer capable of functioning it is advantageous when the kit has at least one guiding element with a guiding piece and a coupling piece, with the guiding piece being designed in such a manner that it can be arranged both rotationally fixedly relative to the tibia part in the bore of the tibia part and can also be rotationally fixedly connected to the bearing body. The coupling piece is rotatably journalled in the guiding piece and has a stabilizing piece which reaches between the condyles of the femur part in order to cooperate there with a stabilizing element. With this, posteriorly stabilized prosthesis types with additional varus/valgus stabilization (when collateral ligaments which are capable of functioning are absent) can be realized.
The stabilizing, element at the femur part comprises in an advantageous variant embodiment a connection web which is formed in the manner of a wall and which together with two side walls forms a box which is arranged between the two condyles of the femur part and which cooperates with the guiding surface of the guiding element or with the stabilizing piece of the coupling piece of the guiding element respectively. Depending on which type of knee joint prosthesis the connection web which is formed in the manner of a wall cooperates with, during the flexion either the outer wall of the connection web which is formed in the manner of a wall enters into contact with the guiding surface of the guiding element, or else the inner wall of the connection web which is formed in the manner of a wall enters into contact with the guiding surface of the coupling piece of the guiding element. Moreover, in the last named variant a varus/valgus stabilizing also takes place with the help of the stabilizing piece, which reaches between the condyles of the femur part, and the side surfaces (stabilizing surfaces) of which cooperate with the side walls of the box.
In a preferred exemplary embodiment the kit in accordance with the invention comprises all the above-listed elements. A kit of this kind is distinguished by its extremely high degree of flexibility, which means that dependently of the respective indication the different prosthesis types can be put together in a modular manner from this kit. A particular advantage in this is that this flexibility is also intra-operatively present, which means that in cases in which he finds special anatomical conditions during an operation in spite of careful pre-operational planning, the orthopedist can still select that prosthesis type from the kit which is best suited for the respective application and put it together during the operation. This high degree of flexibility is advantageous in particular because e.g. the state of the ligaments cannot always be determined with absolute certainty in spite of careful pre-operational planning or else the bone material is actually in a better or worse condition than the pre-operational analysis indicates, so that a prosthesis type which is different from the originally pre-operationally planned prosthesis type appears to be indicated instead.
Since the tibia part in accordance with the invention can be combined in a modular manner with the other components of the kit to form a plurality of functionally different prosthesis types, the number of the tibia parts in the kit can be kept relatively low. At most four tibia parts of different kinds are preferably present in the mentioned preferred exemplary embodiment of the kit, namely two for cemented and two for cementless knee joint prostheses, with in both casesxe2x80x94cemented and cementlessxe2x80x94in each case one tibia part being provided for fixed bearing bodies and one for mobile bearing bodies. The tibia parts which are provided for cemented prostheses on the one hand and for cementless prostheses on the other hand do not differ in their geometrical design. The tibia parts for cemented prostheses have cement pockets at their lower side facing the tibia. In the tibia parts for cementless prostheses no cement pockets are provided, but instead the tibia part is provided at the lower side facing the tibia with a material coating which furthers the growing in of the bone, for example with porous titanium. This can take place in the manufacturing technology in such a manner that the tibia part for cementless applications can be won from tibia parts for cemented applications in such a manner that the cement pockets are filled with porous titanium.
The method in accordance with the invention for implanting a knee joint prosthesis comprises the following steps:
Selection of a suitable prosthesis type;
Resection of the tibia and of the femur in accordance with a predetermined execution of the cutting;
Selection of a tibia part from the kit in accordance with the invention;
Fixing the tibia part to the tibia;
Selection of a femur part from the kit which is suitable for this prosthesis type;
Fixing the femur part at the femur;
Selection of a bearing body from the kit which is suitable for the prosthesis type;
Insertion and where appropriate fixing of the bearing body.
The orthopedist can, after the selection of the suitable prosthesis type and resection of the tibia in accordance with a predetermined execution of the cutting, which is the same for all tibia parts, select a tibia part, fix the latter to the tibia, then select a corresponding femur part, fix the latter at the femur and finally select a suitable bearing body and insert it. Should it turn out during the operation that as a result of the anatomical conditions another prosthesis type is indicated instead, then the orthopedist can still intra-operatively decide on another type of knee joint prosthesis. In tibia parts for fixed bearing bodies he still has e.g. the choice between a bearing body with normal or particularly high congruence; in tibia parts for slidingly displaceably journalled and/or rotatably journalled bearing bodies he still has the choice among an entire spectrum of prosthesis types. This will be described in detail below.
In the method in accordance with the invention for the revision of a knee joint prosthesis with the help of a kit in accordance with the invention the following steps are carried out:
Decision whether the same prosthesis type is retained or a change is made to another prosthesis type;
Selection of a bearing body from the kit which is suitable for the selected prosthesis type;
Insertion and where appropriate fixing of the bearing body while retaining the original tibia part and/or the original femur part.
The orthopedist can thus first decide whether as a result of the anatomical conditions the same prosthesis type is retained or another prosthesis type should be used. The latter is clearly the more frequent case in revisions. Then the orthopedist can decide whether for the new prosthesis type the original femur part and/or the original tibia part can be retained, which depends among other things on the prosthesis type on which the orthopedist decides during the revision. Then the orthopedist can select from the kit in accordance with the invention a bearing body which is suitable for the selected prosthesis type and then insert the new tibia part or the new femur part or elsexe2x80x94in the event that the tibia part and the femur part are retainedxe2x80x94insert only the new bearing body.
In the following the invention will be explained in more detail both in regard to the apparatus and in regard to the method with reference to the drawings and with reference to exemplary embodiments.